This is many serious speaker builders' most favorite damping material that absorbs sound reflections as well as dampens cabinet resonance.

Asking $33 plus actual shipping cost. This means about $2.5 per sq ft. Original price is $3.75 / sq ft. Compare this to No Rez (about $8.4 / sq ft) and to PE's Sonic Barrier (260-530; about $5 / sq ft). You will need to use adhesive to apply it. 3m Hi-strength 90 spray adhesive, or vibration-resistant glue such as Amazing Goop or Shoe Goo also works very well.